1. Field of the Invention
The present invention relates to a hybrid compressor for use in combined internal combustion and electric vehicles. In particular, the invention relates to a hybrid compressor which may be driven by an internal combustion engine or an electric motor.
2. Description of Related Art
A hybrid compressor capable of being driven by an internal combustion engine of a vehicle or an electric motor, or both, is described in Japanese Utility Model (Laid-Open) No. 6-87678. This hybrid compressor includes a clutch for the connection and disconnection of the compressor to an internal combustion engine of a vehicle and to an electric motor, and a single compression mechanism capable of being driven by the engine or the electric motor, or both.
Nevertheless, the hybrid compressor described in Japanese Utility Model (Laid-Open) No. 6-87678 is subject to several disadvantages. First, because a rotor of an electric motor is rotated when the engine is driven, the moment of inertia of a rotational portion is significant and an energy loss is significant. Second, in a case in which the electric motor is a DC brushless motor having a magnet, when the engine is driven, a rotational resistance loss is generated. This loss may be ascribed to the magnet. Third, in order to drive a compression mechanism, which is being driven by an engine, by an electric motor, a large-torque electric motor must be used, or the compression mechanism must be formed as a variable displacement-type mechanism which is capable of being driven even by a low-torque electric motor. Consequently, the size and complexity of the compressor increases. Fourth, when driven by an electric motor, such compressors experience significant energy loss and generate noise. Fifth, when driven by an electric motor, a drive shaft, which projects outside of the compressor's casing so that an engine also may drive the compressor also rotates or continues to rotate. When the drive shaft rotates, an energy is lost due to frictional resistance created by a shaft sealing device for the drive shaft, such as a lip seal, and the driving efficiency of the electric motor decreases. Sixth, because the same compression mechanism is driven by an engine and an electric motor, it is difficult or impossible to operate each drive source at a maximum efficiency.